Approach Considerations
Diagnosis of anaplastic thyroid carcinoma (ATC) requires cytologic examination of tumor tissue. Fine-needle aspiration often yields enough cytologic information to allow diagnosis; however, if the fine-needle aspiration does not provide definitive results, the patient may require an open surgical biopsy.
ATC cannot be definitively diagnosed with laboratory examinations of the blood or urine. Obtain serum calcium levels to rule out medullary thyroid carcinoma or parathyroid neoplasms. Imaging studies are used to assess local spread and distant metastasis.
Molecular Testing
Although the 2012 American Thyroid Association guidelines do not advocate molecular testing of anaplastic thyroid carcinoma tumors, selective BRAF inhibitors are being tested in patients with BRAF-mutated anaplastic thyroid carcinoma and may hold promise. [2] Uncommon genetic mutations, such as TSC1 mutation and ALK rearrangements, have reportedly responded to everolimus and crizotinib, respectively, in patients with ATC. [11, 12] Thus, molecular testing is needed to identify mutations for targeted therapy. Because molecular testing can take 2 to 3 weeks to complete, this test needs to be peformed as quickly as possible.
Imaging Studies
Ultrasonography is an essential imaging technique for evaluation of thyroid masses and is used to guide fine-needle aspiration cytologic and core needle biopsy procedures. The dominant sonographic findings of ATC are heterogeneous echogenicity, an irregular shape, an uncircumscribed margin, hypoechogenicity, and solitary nodules. [13] Preoperative cervical ultrasonography can detect lymph node metastases.
Chest radiography may be used to determine the presence of lung metastases.
Cervical CT scanning can be used to define the local spread of disease. Detection of distant metastases to the mediastinum, liver, lung, bone, and brain is also possible via CT scanning or MRI.
Bone scanning can be used to determine the presence of bone metastases.
Positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG) can visualize primary tumors, lymph node metastases, lung metastases, and other distant metastases. [14]
Histologic Findings
Grossly, anaplastic carcinoma of the thyroid (ATC) is a large, fleshy, off-white tumor. Infiltration of adjacent structures can be observed grossly and microscopically. Histologically, the tumor may contain regions of spontaneous necrosis and hemorrhage. Typically, angioinvasion is detectable.
The main histologic variants include spindle cell, giant cell (osteoclastlike), squamoid, and paucicellular. The giant cell subtype typically exhibits local calcification with significant osteoid formation. The paucicellular subtype demonstrates rapid growth, intense fibrosis, focal infarction, diffuse calcification, and encroachment of adjacent vascular tissue by atypical spindle cells.
Thyroid lymphoma is the only curable condition that may be confused with ATC. Rule out lymphoma in the presence of a poorly differentiated large cell thyroid tumor. This investigation involves lymphoid tissue markers (eg, cytoplasmic immunoglobulin, immunoglobulin receptors, gene rearrangement studies).
Staging
All patients with anaplastic thyroid carcinoma are classified as having stage IV disease, because of the high mortality of the disease. Stage subdivisions are as follows:
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Stage IVA – Intrathyroidal tumors
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Stage IVB – Extrathyroidal tumors but no distant metastatic disease
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Stage IVC – Distant metastasis
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Algorithm for the management of a solitary thyroid nodule. FNAB = fine needle aspiration biopsy; US = ultrasonography.
